This invention relates to apparatus and methods for making intraoperative orthopedic measurements. More particularly, this invention relates to apparatus and methods for making measurements during an orthopedic medical procedure that are related to, for example, the positions and orientations of a patient's bones.
There are many orthopedic medical procedures in which it is necessary for a surgeon to make relative measurements of the positions and orientations of a patient's bones. A surgeon may make such measurements, for example, to assist in placing a patient's bones in the appropriate relationship to one another at the termination of an orthopedic medical procedure. The relative measurements of the positions and orientations of a patient's bones provide the surgeon with a differential measurement, which is defined as the difference between a current relative position and orientation of the bones (i.e., the relative position and orientation of the bones at some time during an orthopedic medical procedure) and the initial relative position and orientation of the bones (i.e., the relative position and orientation of the bones prior to the orthopedic medical procedure). The surgeon can use the differential measurement to, for example, return the patient's bones to their initial relative position and orientation at the termination of the orthopedic medical procedure. In another example, the surgeon can use the differential measurement to place the patient's bones in a relationship to one another that is different than the initial relative position and orientation to correct an existing anatomical problem.
Historically, orthopedic surgeons have used various devices to determine a differential measurement. For example, surgeons have used mechanical measurement devices to determine a differential measurement. However, mechanical measurement devices can be affected by measurement ambiguity and are typically invasive, thereby causing additional trauma to a patient by securing various components of the devices to the patient. Furthermore, many of these devices require the patient either to remain in a fixed position during the procedure or to return to a particular position prior to the termination of the procedure to determine a differential measurement. However, since a patient is typically shifted from an initial position during the procedure, either holding the patient in a fixed position or returning the patient to a particular position can be difficult.
In another example, surgeons have used devices such as positional measurement devices to determine a differential measurement. Positional measurement devices provide a surgeon with greater accuracy in determining the differential measurement than the mechanical measurement devices described hereinabove. However, the existing positional measurement devices are large, thereby restricting a surgeon's motion during an orthopedic medical procedure, and costly. Illustrative positional measurement devices are described in, for example, Horbal et al. U.S. Pat. No. 5,249,581 and Marmulla U.S. Pat. No. 6,241,735.
A total hip arthroplasty (“THA”), also known as a hip joint replacement procedure, is an example of an orthopedic medical procedure that benefits from making intraoperative orthopedic measurements. Mechanical measurement devices for making orthopedic measurements in hip joint replacement procedures have the drawbacks as outlined hereinabove, such as measurement ambiguity and invasiveness. An example of a mechanical measurement device for use in a hip joint replacement procedure is described in Benson U.S. Pat. No. 5,603,717.
The existing positional measurement devices for making orthopedic measurements in hip joint replacement procedures have the drawbacks as outlined hereinabove, such as size and cost. In addition, the existing positional measurement devices used in hip joint replacement procedures can require substantial changes to the standard procedure to, for example, accommodate optical sensors used to make the intraoperative orthopedic measurements in some of the positional measurement device systems. In some of the existing positional measurement device systems involving optical sensors, light-emitting diodes (“LEDs”) are used as bone markers. (An example of a positional measurement device system involving LEDs is described in DiGioia, III et al. U.S. Pat. No. 6,002,859.) The LEDs require an unobstructed line of sight to the optical sensor device. This forces the surgeon to perform the hip joint replacement procedure from what is often a sub-optimal location. In addition, the LED bone markers need to be attached in multiple positions on the patient, which can be difficult since the bone markers are relatively large and the exposed bone area is relatively small.
Accordingly, it would be desirable to provide improved apparatus and methods for making intraoperative orthopedic measurements that are related to, for example, the positions and orientations of a patient's bones.